Cap stable fits can be tricky to set up, to really help you we need to see at least one of your fits.
We also need to know what you are going to use the ship for and whether you prefer to be in close and brawl or a sniping fit that works from range.
Size of the booster is critical as well as the type. It is often possible to make a BS cap stable with a LSB but not with a XLSB. I have seen many cap stable mission fit BS that run a MSB instead of the LSB or XLSB.
Another concept to learn is a something in my corp we refer to as functional cap stability. For this the fit is not truly cap stable, however it has enough cap to last most of the way through a typical mission, when you combine that with pulse tanking see below the ship becomes functionally stable and that is really all you need.
It is possible to run missions even level 4’s with a ship that has as little as 2 minutes cap as long as it is stable with your booster turned off using a method know as pulse tanking. Turn booster on to rep damage, then turn it off and allow your cap to re-charge.
[Rattlesnake, Tech 2]
Cruise Missile Launcher II_2, Inferno Fury Cruise Missile
Cruise Missile Launcher II_2, Inferno Fury Cruise Missile
Cruise Missile Launcher II_2, Inferno Fury Cruise Missile
Cruise Missile Launcher II_2, Inferno Fury Cruise Missile
Cruise Missile Launcher II_2, Inferno Fury Cruise Missile
Large Remote Armor Repairer II
Shield Recharger II_2
Shield Recharger II_2
Shield Recharger II_2
Large Shield Extender II_2
Adaptive Invulnerability Field II_2
EM Ward Field II_2
Adaptive Invulnerability Field II_2
Drone Damage Amplifier II_2
Drone Damage Amplifier II_2
Drone Damage Amplifier II_2
Shield Power Relay II_2
Shield Power Relay II_2
Shield Power Relay II_2
Large Capacitor Control Circuit I_2
Large Core Defense Field Purger II_2
Large Core Defense Field Purger II_2
Drones to suit your needs / wants / desires
This is just one idea of how to make a Rattlesnake cap stable.
For the T2 mods there are some skills that would need to be trained to level 5 to be able to fit & fly.
All other skills that affect this fit were set to level 4.
Brawler fit because we like to fly it that way because it is different than most and it is fun.
Passive tank so the only tank mods to turn on / off are the resistance mods.
20 minutes tank with everything running but the remote rep.
Once some of the incoming DPS has been killed off turning off one resist mod makes this cap stable without the remote rep.
Remote rep is only used as needed, generally between pockets and sometimes between groups within a pocket to repair damaged drones.
With all applicable skills trained to level 5 and the remote rep turned off this is also cap stable.